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Honda is the most important bike producer by an enormous margin, and so they’re one of many largest automotive producers too. They’ve constructed Method 1 vehicles, jet plane, robots, boat engines, and plenty of energy tools.
The corporate channels round 6% of their annual income into analysis and growth, making them notably well-known for its innovation.
However Honda’s innovation isn’t simply restricted to merchandise with motors. 20 years in the past, they had been experimenting with some top-secret bicycle gearbox drivetrains. And after a handful of seasons on the downhill World Cup MTB circuit, the Honda gearbox bikes had gained the world championships and 5 World Cup rounds.
Sadly for us, the gearboxes that Honda developed had been by no means meant to be industrial merchandise. It turned out that Honda poured cash into this program purely to problem the minds of their engineers.
Because the patents on these gearboxes are expiring quickly, I believed this may be a good time for us to analyse all three generations of the Honda bicycle gearboxes. You’ll study concerning the designs and the way all of them work, we’ll look at why there aren’t extra gearboxes following comparable designs, and we’ll look into the subsequent technology of gearboxes on this house.
However first, let’s discover out the benefits and drawbacks of utilizing a gearbox over a derailleur drivetrain for mountain bike racing.
The Benefits of a Gearbox Drivetrain for Racing
One huge benefit on a downhill race bike is the reliability increase by way of extra floor clearance. Derailleurs dangle low on a motorcycle and are prone to break from rocks, sticks and crashes. On a short-timed run, a damaged derailleur, or a missed shift, could be the distinction between successful and shedding.
Moreover, a gearbox has the flexibility to immediately shift gears with out the necessity to pedal. This enables riders to pre-load the right gear earlier than a nook, within the air, or whereas using via a rock backyard.
Talking of tough terrain, by shifting the shift elements to the centre of the bike, the rear suspension efficiency could be improved resulting from a discount in unsprung mass on the rear wheel. This enables the rear suspension to react quicker, growing traction, and the bike may deal with higher with the load central and low.
A modest increase in efficiency may be present in hostile using circumstances. Derailleurs and jockey wheels can get jammed with mud and grit, affecting their skill to shift or function effectively. A gearbox seals away many of those vital drive elements.
However actually, the most important benefits of bicycle gearboxes are realised on the shopper degree, as you get an extremely low-maintenance drivetrain, that’s climate resistant, crash resistant, and with fewer elements that can put on.
Why Are Derailleurs Nonetheless Widespread in Racing?
Merely put, derailleur drivetrains are the lightest gear system with the very best drive effectivity, which in bike racing, is the right recipe for successful. Because of this virtually all bicycles raced on the high degree use derailleurs.
Mountain bikes with derailleur drivetrains are, at minimal, one to 2 kilograms lighter than gearbox bikes (2.2-4.4lb). Derailleurs may switch extra of your pedal energy to the rear wheel – it really works out at round 5% extra energy than for those who had been utilizing a Pinion gearbox (in preferrred using circumstances) however this quantity can slender relying on the facility output and cadence of the rider, together with the using circumstances, lubricants used, chain contaminants, drivetrain put on, and far more.
As well as, derailleurs enable for a really broad variation in bicycle body design, as a rear hanger is the one essential infrastructure for putting in gears on a motorcycle. As compared, the packaging necessities of a gearbox considerably restrict the flexibility of a body designer to optimise the suspension structure.
And lastly, derailleur drive elements could be shortly and simply changed, which is good for mechanics who’ve restricted time for race repairs. And it’s much more preferrred for derailleur producers who actually like promoting derailleurs.
Proper, let’s get into what you’re actually right here for – the Honda gearbox tech!
The Honda CVT Gearboxes
The primary two Honda gearbox generations are, by far, probably the most fascinating – however sadly, there are only a few pictures and restricted details about them outdoors of their patent.
Whenever you consider a bicycle gearbox, you usually consider huge spur gears meshing on the crankset (Pinion), or a lot finer planetary gears rotating round solar gears inside a rear hub (Rohloff, Shimano).
The primary two generations of Honda gearboxes had been neither. And so they didn’t even have set gear ratios! They as a substitute used a camshaft and a collection of levers to vary the drive ratio.
Only a few individuals knew of those gearboxes, and even fewer understood how they labored. Stick round till the tip and I assure a cam and lever bicycle gearbox will make sense to you.
Why did Honda design their earlier gearboxes this manner?
Firstly, you bought to select from an infinite variety of gears between two set factors – this is called a constantly variable transmission, or CVT. Shifting was instantaneous, and the gearbox would by no means ‘skip’ like a poorly-tuned derailleur.
The CVT gearbox was additionally notably compact by the second technology – virtually half the amount – and in idea, might be fairly environment friendly too.
Sadly, the Honda CVT packing containers had been seen only a handful of occasions at bike races and commerce exhibits, and had been by no means raced on the World Cup circuit. We are going to by no means know why Honda shelved these earlier gearboxes, however that’s okay as a result of that they had one other gearbox able to go.
The Honda Derailleur in a Field
The G Cross Honda group burst onto the downhill World Cup circuit in 2004 with a bunch of gifted riders. The Honda bike ended up successful the primary World Cup race it was entered in, immediately proving the carbon-shelled gearbox was the actual deal.
For greater than a yr, we might solely guess what was contained in the third-generation gearboxes, as they had been racing with them lengthy earlier than anybody was allowed to look inside. In reality, Honda mechanics carried out all gearbox upkeep hidden from view, and the gearboxes had been by no means saved with the bikes. As a substitute, the gearboxes stayed inside resort rooms with the mechanics to not solely forestall theft however to maintain the design a secret.
After the patents had been ultimately made public, we discovered that the newest gearboxes had been nothing notably genius. The answer was a derailleur-in-a-box: a 7-speed gear system that used the identical elements as a daily drivetrain, however was all sealed away from the weather.
Whereas not as revolutionary because the CVT packing containers, the inner derailleur drivetrain nonetheless achieved Honda’s targets of shifting with out pedalling, lowering the unsprung mass on the rear wheel, and making a gear system that was much less prone to break.
The gearbox labored by transferring pedal energy right into a sprocket positioned on the crank spindle. When this sprocket turned, it will drive the inner chain onto a small cassette the place the gear ratio was chosen. The cassette then straight drove the exterior sprocket, which went on to drive the rear wheel.
The freewheel for this drivetrain was positioned on the crank spindle, which meant that each time the rear wheel was shifting, the inner chain was operating, and the gears might be modified with out pedalling.
A very cool factor about this miniaturised derailleur drivetrain was that the chain line was at all times straight as a result of each the sprocket on the crank spindle and the derailleur moved in unison whenever you shifted.
A straight chain line is vital for guaranteeing a excessive drive effectivity – some fast maths suggests this drivetrain would possible function inside 2% of a daily derailleur setup, but it surely might be extra environment friendly in hostile circumstances.
Whereas the Honda gearbox was refined and race-proven virtually 20 years in the past, it’s value noting that PeteSpeed had a very comparable patented gearbox on bikes at across the identical time. This design was later licensed by Hayes, however I don’t assume it ever made it onto any manufacturing bikes.
The Downsides of a Derailleur in a Field
As a derailleur-in-a-box makes use of present bike elements and gives a excessive drive effectivity, it looks like a perfect resolution for a gearbox bike. So, why aren’t bike producers engaged on this tech for customers?
One challenge is the bodily dimension of the gearbox – when the field turns into too massive, it significantly limits body design. Simply look how huge the Honda field was when it was utilizing a tiny highway bike cassette with simply over 200% gear vary. If we had been to squeeze in a contemporary cassette from a 1X drivetrain (eg. 10-52t), it will be monstrous!
To maximise bike compatibility, gearboxes are at present being designed round eBikes in addition to common bikes. With the additional packaging constraints of a motor and battery, this makes a derailleur-in-a-box even much less commercially viable.
However regardless of these downsides, persons are nonetheless forging on with this idea.
The Subsequent Era
Williams Racing Merchandise has just lately been teasing a working prototype of a derailleur in a field. This design is impressively compact, and would possibly even match a standardised body design sooner or later. However once more, the gear vary is restricted to the cassette dimension that can match inside their field.
Cesar from UNNO bikes holds a latest patent for the same gearbox, so there are possible working prototypes in existence. The fascinating factor is that there isn’t a derailleur inside this gearbox, as a substitute, it’s the cassette that slides backwards and forwards. That is cool, but it surely creates additional packaging points because of the additional gearbox width.
Three years in the past, I made an in-depth video about Shimano’s 13-speed gearbox patent that makes use of a type of derailleur. Once more, a really cool design, however proper now in 2023, there aren’t any updates on its growth.
And Nicolai bikes have at all times been tinkering with gearboxes, nevertheless, the newest derailleur-in-a-box prototypes are actually a decade outdated.
Okay, let’s swap gears for a bit, and learn how Honda’s first and second gen CVT gearboxes labored. I believe you’ll discover this bit notably fascinating!
How Does the Honda CVT Gearbox Work?
Observe: this part is finest watched in my Honda gearbox video (11:18) because the visuals will assist lots.
Right here’s a cross-section of the CVT gearbox to assist us perceive it. The crankset is positioned down the underside and the output sprocket is positioned up the highest.
We will break the gearbox into three key sections:
The first part will increase the rotation velocity of the sprockets contained in the gearbox. This enables the ultimate sprocket to spin about 11x quicker than the crankset – which means this gearbox strikes at round 1,000RPM underneath a typical rider cadence (90RPM).
The velocity of the sprockets is elevated utilizing three gear units: one from the crank spindle to a separate meeting, one other gear set again the crank spindle, and one other to a particular sprocket housed on a camshaft.
The second part is all about turning rotation right into a repetitive linear motion utilizing a camshaft. The final sprocket from the primary part of the gearbox is related to an eccentric cam, so each time it spins, a collection of 4 connecting hyperlinks can transfer up and down. One of the best ways to grasp what’s occurring right here is to think about a piston going up and down.
We now want to have a look at a line drawing to grasp what occurs subsequent, and that is the place it will get a bit tough to observe. The decrease hyperlink is the camshaft, and the higher hyperlink is related to the ultimate part of the gearbox, the one-way clutch. Each time the camshaft strikes up and down, it strikes the higher hyperlink up and throughout, alongside a round path.
The remaining part is all about turning our reciprocal motion again to rotary motion. Because the higher hyperlinks transfer on a round path, Honda employed a one-way clutch in order that solely the rearward motion would drive the exterior sprocket, whereas the ahead motion would merely “freewheel” – to place it into bike phrases. This clutch would function equally to an Onyx rear hub, providing instantaneous engagement.
However right here’s the place issues get loopy. Our exterior sprocket wouldn’t transfer in a very clean movement if the clutch is continually participating and disengaging, so the geniuses at Honda designed a wavy gear set that may offset these oscillations.
And what concerning the infinite gears?
Effectively, a twist shifter on the handlebar adjusted the geometry of the drive hyperlinks. When the shift actuator arm was excessive – as proven on this higher gearbox line drawing – the camshaft pushed the clutch a shorter distance per rotation than when the shift actuator arm was down. The gap the clutch moved within the highest gear was about 3x additional than the bottom gear – leading to a ~300% gear vary.
The geometry of the hyperlinks might be manipulated wherever between these two factors when shifting, and that is what offers us an infinite variety of gear choices.
Abstract
20 years in the past, Honda did one thing very spectacular. To create a gearbox bike that might sustain with derailleur bikes on the high degree was unprecedented again then, and hasn’t been achieved since.
Their derailleur-in-a-box design was so easy and efficient in execution, I’m shocked we haven’t seen it replicated in downhill mountain bike racing the place the design clearly works.
That stated, the Honda and PeteSpeed patents expire quickly, and we’re seeing new prototypes coming via – so maybe the subsequent derailleurs-in-boxes are nearer than not.
The primary and second-generation CVT gearboxes had been actually revolutionary, with their camshafts, hyperlinks and one-way clutches. I’d like to know why the thought wasn’t pursued additional, however I believe that’ll keep as Honda’s little secret.
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